Stratigraphy and depositional evolution of the uppermost ... · order to establish a new...

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Stratigraphy and depositional evolution of theuppermost Oligocene – Miocene succession in westernDenmark

ERIK SKOVBJERG RASMUSSEN

Rasmussen, E.S. 2004–12–15: Stratigraphy and depositional evolution of the uppermost Oligocene –Miocene succession in western Denmark. Bulletin of the Geological Society of Denmark, Vol. 51, pp.89–109. © 2004 by Geological Society of Denmark. ISSN 0011–6297.

The uppermost Oligocene – Miocene succession in Denmark is subdivided into six depositionalsequences. The development of the succession was controlled both by tectonic movements andeustatic sea-level changes. Tectonic movements generated a topography, which influenced thedepositional pattern especially during low sea level. This resulted in sediment by-pass on elevatedareas and the confinement of fluvial systems to structural lows. Structural highs further created re-stricted depositional environments behind the highs during low sea level. The structural highs werealso the locus for sandy spit deposits during transgression and high sea level. Initially sedimentsupply was from the north and north-east but shifted within the Middle Miocene to an easterly di-rection indicating a significant basin reorganisation at this time. Eustatic sea-level changes mainlycontrolledthe timingofsequence boundary development and the overall architecture of the sequences.Consequently, the most coarse-grained sediments were deposited within the forced regressive wedgesystems tract, the lowstand systems tract and the early transgressive systems tract. The most dis-tinct progradation occurred in the Aquitanian (Lower Miocene) and was associated with a cold pe-riodincentralEurope.Thesubsequentriseofsealeveluntil theSerravallian(Middle Miocene) resultedin an overall back-stepping stacking pattern of the sequences and in decreasing incision.

Keywords:Oligocene,Miocene,NorthSea,Denmark,eustacy,climate, tectonics,sequencestratigraphy.

Erik Skovbjerg Rasmussen [[email protected]], Geological Survey of Denmark and Greenland, Øster Voldgade10, DK-1350 Copenhagen K.

The uppermost Oligocene – Miocene succession inDenmark has been studied intensively in pits andboreholes during the past sixty years, and a numberof lithostratigraphic units have been defined (Sor-genfrei 1940, 1958; Larsen & Dinesen 1959; Rasmus-sen 1961; Christensen & Ulleberg 1974). However, acompilation of these lithostratigraphic units hasnever been published. The most commonly usedlithostratigraphic schemes in various publicationsabout the Miocene in Denmark are that of Rasmus-sen (1961), Buchardt-Larsen & Heilmann-Clausen(1988) and Michelsen (1994).

Systematic studies of seismic data and wells fromthe North Sea has significantly increased during thepast 10 years and thus the understanding of the geo-logical evolution of the eastern North Sea area (Jordtet al. 1995; Michelsen et al. 1998; Clausen et al. 1999).Attempts to correlate the depositional sequenceswithin the North Sea have been made by Michelsen(1994) and Michelsen et al. (1998) but due to poor

biostratigraphic resolution of outcrop sections (dis-solution of foraminifera) only a tentative correlationhas been possible. The finding of dinoflagellates,which appear at flooding surfaces throughout the up-permost Oligocene – Miocene succession at outcropsin Denmark (Dybkjær & Rasmussen 2000), has re-sulted in a confident and consistent onshore and off-shore correlation of the succession. A number ofstratigraphic boreholes and high resolution seismicdata were acquired in eastern and central Jylland inorder to establish a new stratigraphic subdivision ofthe uppermost Oligocene – Miocene succession on-shore Denmark.

The aim of this study is to establish a stratigraphicframework for genetically related depositional pack-ages that can form the basis for a new lithostrati-graphic subdivision of the succession. Finally, theprocesses involved in the deposition of the succes-sion will be discussed.

Rasmussen: Stratigraphy and evolution of the Oligocene–Miocene succession in western Denmark ·

90 · Bulletin of the Geological Society of Denmark

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Fennoscandian Shie ld

nniissaaBB

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Fjerritslev Fault

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S o r g e n f r e i To r n q u i s t Z o n e

N o r t h G e r m a n B a s i n

Ringkøbing

0 100 km

Limitation of high

Normal fault

Inferrednormal fault

Salt pillow

Salt diapir

Shoreline(Aquitanian)

Elevatedareas

Centra l G

raben

Horn Trough

Fyn High

RomeleFault

56 N

56 N

57 N

55 N

55 N

10 E

10 E5 E 15 E

Bran

de Tro

ugh Fyn High

Romele Fault

Fig. 1. Structural elements of the Danish North Sea area. Modified after Bertelsen (1978) and Vejbæk (1997).

Hodde Formation

Arnum Formation

Klintinghoved Formation

Odderup Formation

Ribe Formation

Upper Miocene

Middle Miocene

Lower Miocene

L I T H O S T R A T I G R A P H Y

Gram Formation

West East

CHRONO-STRATIGRAPHY

Marine deposits Fluvio-deltaic deposits

Odderup Formation

Ribe Formation

Fig. 2. Lithostratigraphic scheme for the Miocene of Denmark (after Rasmussen 1961).

91

Geological settingThe development of the eastern North Sea area dur-ingtheCenozoic was the result of reactivation of olderMesozoic structural elements and subsidence due tothermal relaxation and interplate stress (Kooi et al.1991; Ziegler 1991). The deepest part of the basin waslocatedin the Central Graben area, whereas the north-eastern border was strongly controlled by the Fen-noscandian Border Zone also known as the Sorgen-frei–Tornquist Zone (Fig. 1). The Ringkøbing–FynHigh, which divides the Norwegian–Danish BasinandtheNorth German Basin, formed an elevated ele-ment with pronounced halokinetic movements bothnorth and south of the structure. The Alpine Orogenyinfluenced the basin as well as the opening of theNorth Atlantic also influenced the evolution of theNorth Sea area (Clausen et al. 2000). Inversion re-sulted in uplift along weakness zones within the Cen-tral Graben and along the Fennoscandian BorderZone/Sorgenfrei–Tornquist Zone during the Pale-ocene (Liboriussen et al. 1987; Ziegler 1991; Mogensen& Jensen 1994). Compressional tectonics in the Olig-ocene and Miocene, related to the collision of Africaand Europe, have also been recognised (Jordt et al.1995; Michelsen et al. 1998; Clausen et al. 2000). Theimportance of eustatic sea-level changes during theOligocene and Miocene has been documented froma number of studies (Rasmussen 1996, 1998; Huuse& Clausen 2001).

The siliciclastic infilling of the North Sea area be-gan in the Late Paleocene (Heilmann-Clausen et al.1985). In the Norwegian–Danish Basin the Paleocenedeposits are dominated by clay, but sand-rich grav-ity sediments were laid down in submarine valleysin the North Sea area (Danielsen et al. 1995). The de-position of dominantly fine-grained sediments con-tinued throughout the Eocene, however, with someindication of major progradation from the MiddleEocene. Clear evidence for progradation of majorsiliciclastic systems and the influx of coarse-grainedsediments is documented from the Oligocene (Jordtet al. 1995; Michelsen et al. 1998). The progradationalsystem was sourced from the western part of theFennoscandian Shield and prograded southward.This pattern continued throughout the Oligocene andEarly Miocene (Clausen et al. 1999; Rasmussen et al.2002). The southward prograding system with adominantly south-east – north-west trending shore-line can be recognised on onshore seismic data andin outcrop sections in eastern Jylland (Rasmussen etal. 2002). The onshore studies suggest that thedepositional environment was related to spit systemsand lagoons on and north of the Ringkøbing–FynHigh with more open marine conditions towards the

south (Larsen & Dinesen 1959; Christensen & Ulle-berg 1974; Rasmussen 1996; Friis et al. 1998). How-ever, this general picture was punctuated by displace-ment of the shoreline during lowstand of sea levelespecially in the lowermost Miocene (Aquitanian;Rasmussen 1996, 1998; Dybkjær & Rasmussen 2000).A distinct change in sediment supply occurred inmid-Miocene that may be due to regional tectonicre-organisation related to the Betic tectonic event(Clausen et al. 1999). The coincidence of this tectonicphase and a distinct eustatic sea-level rise during theSerravallian (Middle Miocene) (Prentice & Matthews1988) resulted in major flooding and retreat of theshoreline. Consequently, clay-rich deposits were ac-cumulated in the study area. Evidence of resumednearshore deposition in the eastern North Sea areais first recognised in the Pliocene approximately 9Ma years later (Gregersen et al. 1998).

Uppermost Oligocene – MiocenelithostratigraphyA number of papers have defined lithostratigraphicunits of the uppermost Oligocene – Miocene succes-sion in Denmark (Sorgenfrei 1940, 1958; Larsen &Dinesen 1959; Rasmussen 1961; Christensen & Ulle-berg 1974).

The uppermost Oligocene – ?Lower Miocene claysand sands are referred to the Vejle Fjord Formation(Larsen & Dinesen 1959). This formation consists ofmarine sediments and based on lithology it has beensubdivided into the Brejning Clay Member, the VejleFjord Clay Member and the Vejle Fjord Sand Mem-ber (Larsen & Dinesen 1959; Heilmann-Clausen1995). Christensen & Ulleberg (1974) defined theUlstrup and Sofienlund Formations in northernJylland. These formations are, however, normallyincluded in the Vejle Fjord Formation (Buchardt-Larsen & Heilmann-Clausen 1988).

The Miocene succession of Denmark consists ofsix formations (Fig. 2; Rasmussen 1961). The Lower– Middle Miocene marine clays are referred to theKlintinghoved and Arnum Formations, whereas thefluvio-deltaic sediments are referred to the Ribe For-mation and the Odderup Formation. The youngestsediments of the Odderup Formation were depos-ited during the early Middle Miocene. The Middle –Upper Miocene marine, organic-rich, silty clay andglaucony-rich clays are referred to the Hodde andGram Formations (Piasecki 1980).



DANMARKDANMARKDANMARKDANMARK

Vejle Fjord

Kolding Fjord

Lillebælt

200 Km

Norway

Sweden

GermanyEngland

North

Sea

N

∗

∗

∗

∗

∗

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∗

DENMARK

Jensgård

SkansebakkeSanatoriet

PjedstedHvidbjerg

Børup

RønshovedHindsgavl

Hagenør

Dykær

Fig. 4A

Fig. 4B

Fig. 4C

Fig. 10Fyn

Jylland

Addit Mark

Store Vorslunde

Vandel Mark

Egtved Skov

Bastrup

Vejle

Odense

Åbenrå

Billund

Isenvad

Vorbasse

Esbjerg

Gram Gram II

Arnum-1

Rurup

Søndbjerg

Rødding

Grindsted-1

SkjernEg-3

Holsted

Remmerslund

Tønder-3

Løgumkloster-1Borg-1

Brøns-1

0 25 km

New stratigraphic boreholes

Old boreholes

Outcrops

City

Seismic section

Correlation panel

Klovborg

Høruphav-1

9 E

9 E

56 N

Germany

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DataThe study is based on seismic data, gamma logs, sam-ples from new stratigraphic boreholes, washed sam-ples from older boreholes, and sedimentological stud-ies of outcrops in Jylland (Fig. 3).

The following seismic surveys were available forthe study: NP 85, DCJ81, ST87, DN90 and Vorbasse2000. Gamma logs from the boreholes Tønder-3,Borg-1, Løgumkloster-1, Brøns-1, Rurup (DGU-150.642), Gram (DGU-141.852), Rødding (DGU-150.642), Holsted (DGU-141.808), Bastrup (DGU-133.1298), Egtved Skov (DGU-124.1159), Grindsted-1, Grindsted (DGU-122.1342), Remmerslund (DGU-116.1549), Store Vorslunde (DGU-104.2325), Klovborg(DGU-106.1373), and Addit Mark (DGU-98.928) pro-vided data for the correlation diagrams. Biostrati-graphy and samples were available from Høruphav-1, Løgumkloster-1, Brøns-1, Arnum-1, Gram-II, Ba-strup (DGU-133.1298), Store Vorslunde (DGU-104.2325), Klovborg (DGU-106.1373), and AdditMark (DGU-98.928). In addition to these data, geo-logical descriptions from outcrops in eastern Jylland,at Isenvad and Søndbjerg (Rasmussen & Dybkjær1999) and shallow boreholes at Store Vorslunde andSkjern (Knudsen 1998) are included in the study.

Major architectural elements of theMiocene successionThree seismic sections from Jylland and the adjacentoffshore area are used to illustrate the major archi-tectural elements of the uppermost Oligocene – Mio-cene succession (Fig. 4).

Distinct seismic markers are indicated on the seis-mic sections in Figure 4. The base Oligocene markeris a regional unconformity showing truncation of theunderlying succession. From onshore studies insouthern Jylland this unconformity is known to sepa-rate the uppermost Oligocene glaucony-rich BrejningClay Member from the Middle to Upper EoceneSøvind Marl Formation (Heilmann-Clausen et al.1985; Rasmussen 1996). In central and northernJylland the Brejning Clay Member unconformablyoverlies the Upper Oligocene Branden clay (Dybkjæret al. 1999). In the northern part of the seismic sec-tions, where uppermost Oligocene deposits are pre-

sent, the surface correspond to the top occurrence ofthe dinoflagellate species Wetzeliella gochtii (KarenDybkjær, personal communication 2001). Above thebase Oligocene marker, clinoforms show a succes-sive outbuilding from north-east to south-west as il-lustrated by the intra Aquitanian marker (Fig. 4). Acorrelation of the clinoformal break point of the in-tra Aquitanian marker indicates a NW-SE trend ofthe shoreline during the Aquitanian (Lower Mio-cene). Thick deltaic sand was identified in two bore-holes at Vandel Mark penetrating the succession be-low and above the Aquitanian marker. This deltasand can be correlated with a spit system outcroppingin eastern Jylland and referred to the Vejle Fjord For-mation (Larsen & Dinesen 1959; Dybkjær & Rasmus-sen 2000). The intra Burdigalian marker (Fig. 4),which represents the base of the Arnum Formationseparates the succession characterised by a clinofor-mal reflection pattern below from a parallel to trans-parent and sometimes chaotic reflection patternabove (Fig. 4). The resolution of the uppermost partof the seismic section is very poor and therefore can-not add much to the understanding of architecturalelements of the succession.

Sequence stratigraphyThe uppermost Oligocene – Miocene succession hasbeen subdivided into six depositional sequences onthe basis of seismic data, log correlation and lithol-ogy (Fig. 5). The reference level for the log panels isthe sequence boundary between sequences B and C.This level has been chosen because it represents thetime when most structural elements were coveredby sediments and therefore did not influence theoverall architecture of the succession. The lithologyand sequence subdivision of six new stratigraphicboreholes in central Jylland is shown in Figure 6.

Sequence A

Description. The lower boundary corresponds to thebase Oligocene marker on the seismic lines and formsa regional unconformity (Fig. 4). On and south of theRingkøbing–Fyn High this boundary is lithologicallysharp and separates green, glaucony-rich clay abovefrom greenish-grey marl below. North of the Ring-købing–Fyn High the boundary separates glaucony-rich clay from brownish, mica-rich clay. The bound-ary is often evident on the gamma logs as a distinctpeak representing the glaucony-rich deposits over-lying marly sediments (Figs 5, 6).


Facing page:Fig. 3. Map showing the location of outcrops, boreholes, andseismic lines referred to in this study.


S

S

SW

N

N

NE

Bastrup Vandel Mark

Eg-3

Store Vorslunde

base Oligocene marker intra Aquitanian marker intra Burdigalian markerbase Burdigalian marker

A

B

C

Billund delta

1 km100 m

1 km100 m

1 km100 m

Billund delta

Fig. 4. Three seismic lines from Jylland and adjacent areas. Note that the progradation is generally from north to south and thelowering of the offlap level just below the Base Burdigalian marker. For location see Figure 3.

95

Store Vorslunde

Vandel Mark

Addit Mark

Klovborg

Nor

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Rødding

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BASTRUPDGU 133.1298

ClaySand SiltGravel

mbe

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EGTVED SKOVDGU 124.1159

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65

93

105

71

122

178

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150

100

0

VORBASSE

82

103

122

143

166

194

209

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247

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VANDEL MARKDGU 115.1371

22

58

111

141

170

231239

203

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100

50

ST. VORSLUNDEDGU 104.2325

11?

31

55

101

126

160

221

0

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ADDIT MARKDGU 98.928

48

84

103

117

140

163

171

181

00

.

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E

D

D

D

D

C

C

C

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B

A

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B

B

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Eocene

Eocene

Eocene

Oligocene

Eocene Eocene

Eocene

A

97

The lower part of the sequence is characterised bystrongly bioturbated greenish clay, with rip-up clast.The content of glaucony increases upward in the low-ermost metre of the sequence and shells of bivalvesand gastropods are common. In the upper part ofthe section there is an increase in silt and fine-grai-ned sand, and the content of organic matter is gener-ally high. The increasing sand content is reflected onthe gamma log, which shows a general decrease inthe log response in the uppermost part of the unit.The sequence is thin to absent in the southern part ofthe area and increases in thickness towards the north(Fig. 5A).

Interpretation. The lower sequence boundary repre-sentsamajorhiatus inthe succession, especially in thesouthern part of Denmark. On and to the south ofthe Ringkøbing–Fyn High the boundary separates theMiddle Eocene Søvind Marl Formation and upper-most Oligocene Brejning clay. North of the high thelower sequence boundary separates the Upper Olig-ocene Branden clay from the Brejning Clay Member(Larsen&Dinesen 1959; Heilmann-Clausen et al. 1985;Dybkjær et al. 1999; Dybkjær & Rasmussen 2000). Theabundance and diversity of the marine fauna indicateopen marine conditions during deposition of the suc-cession.

The maximum flooding surface is placed were thehighest amounts of glaucony is found (Fig. 5; Amo-rosi 1995, 1997). This corresponds to a distinct peakon the gamma log. Geochemical studies of the glau-cony at this level also show a high potassium contentof theglaucony,which is characteristic for a maximumfloodingsurface(Amorosi1995,1997;Rasmussen1995).

An increase in the proportion of siliciclastic depo-sits relative to glaucony and in terrestrial organic mat-ter above the maximum flooding surface reflects theinitial progradation of a distant shoreline duringhighstand.

Sequence B

Description. The lower boundary is placed at the baseof a thin gravel layer separating glaucony-rich de-posits in the top of sequence A from fine-grained,micaceous and organic-rich deposits at the base ofsequence B (Fig. 5). This change is seen on somegamma logs as a low gamma response followed by amarked increase in gamma response (Fig. 5B;Klovborg at 160 m).

The log pattern of the sequence is characterised

by high gamma readings in the lower part and witha general decrease in gamma log response (Fig. 5). Ahigh degree of lateral variation has been recognisedwithin the sequence. Fine-grained, organic-rich sedi-ments dominate the whole succession in the north-ern part (Fig. 5B; Klovborg and Remmerslund).Sandy deposits are common at Hvidbjerg andLillebælt. In the southern part of Jylland clayey-siltydeposits dominate in the lower part of the sequencewhereas the uppermost part is sand-rich. Approxi-mately 40 m of clean sand has been penetrated in theArnum-1 well (Figs 3, 5). On the gamma log, theuppermost part of the sequence shows very low read-ings, especially close to the upper boundary, wherevalues are extremely low. On seismic sections theupper part of the sequence shows offlap and astepwise lowering of the offlap level (Fig. 4A). In theTønder-3 well (Figs 3, 5) the correlation is based onthe seismic interpretation, which indicates a pinchout of the succession towards the south (Rasmussen1996, 1998).

Interpretation. The base of sequence B correspond toa change in depositional environment from open ma-rine to brackish water documented in a number ofstudies (e.g. Larsen & Dinesen 1959; Dybkjær et al.1999; Dybkjær et al. 2001). The Ringkøbing–Fyn Highprobably acted as a barrier during low sea level (Fig.5). Brackish conditions were established north-eastof the Ringkøbing–Fyn High and the depositional en-vironment was similarly to that reported by Noe-Nygaard & Surlyk (1988) for Lower Cretaceous de-posits on Bornholm. Sedimentological studies of thesuccession reveal that spit systems formed in asso-ciation with structural highs as demonstrated atHvidbjerg and Lillebælt (Rasmussen & Dybkjær1999). North-east of the spit systems, lagoons formedduring the successive transgression and prograda-tion during highstand (Fig. 5; Remmerslund andKlovborg). The maximum flooding surface is placedat a distinct gamma peak (Fig. 5). A palynologicalstudy indicates that dinoflagellate cysts are diverseand abundant at this level (Karen Dybkjær, personalcommunication 2002). Above the maximum flood-ing surface, progradation is seen in the northern partof the study area and is consequently interpreted asa highstand systems tract. The presence of a forcedregressive wedge systems tract in the southern partof the area is indicated by the stepwise lowering ofthe offlap level seen on the seismic panels and thedeposition of extremely clean sand at Arnum-1 (Fig.5). During the time of forced regression the Ringkø-bing–Fyn High was subaerially exposed and a flu-vial depositional environment dominated in this area(Rasmussen & Dybkjær 1999).

Facing page:Fig. 6: Lithology and gamma logs from 6 new stratigraphicboreholes in central Jylland.



Sequence C

Description. The sequence boundary of sequence C isrecognised on the gamma logs by a change from gen-erally decreasing gamma log values towards an up-ward increasing log response. In some boreholes thechange in gamma log response is distinct (e.g. Ba-strup; Figs 3, 5).

In most boreholes the succession immediatelyabove the boundary shows an increase in gamma logreadings indicating a lithological change from sandysilt tomore muddy sediments (Fig. 6). At Bastrup andStore Vorslunde very high gamma readings are rec-ognisedabovetheboundarycorrespondingtoorganic-rich mud immediately above the sequence bound-ary. This is, however, relatively quickly overtaken bya general decrease in the gamma log response reflect-ing an upwards increase in the silt and sand content(Figs 5, 6). At Vorbasse and Egtved Skov abrupt de-creases in the gamma log response are found.

Interpretation. Sequence boundary C is interpreted asa coalescing ravinement surface and sequence bound-ary (Rasmussen 1998; Dybkjær & Rasmussen 2000).The relatively thin interval characterised by a gradualincrease in gamma log readings, most commonly seenin the southern part of the area, is interpreted as atransgressive systems tract with the maximum flood-ing surface placed at the highest gamma log read-ings (Fig. 5). However, at Rødding, Bastrup and StoreVorslunde, the distinct gamma readings represent de-position in a restricted marine environment (KarenDybkjær, personal communication 2001). This partis therefore interpreted as part of the transgressivesystems tract and represents barrier–lagoonal com-plexes. The highstand systems tract is relatively thickand shows progradation of shallow marine sandsover marine silt and clay. The sharp based and cleansand layers in the Egtved Skov and Vorbasse bore-holes are interpreted as sand deposited above a re-gressive surface of erosion and this part of the se-quence thus represent a forced regressive wedge sys-tems tract (Hunt & Tucker 1992; Proust et al. 2002).

Sequence D

Description. In most boreholes the sequence bound-ary is placed where a turnover of gamma log read-ings from a general low gamma log response towardsan overall increasing trend is observed. However, atBastrupandAdditMarktheboundary is placed wherea marked decrease in gamma readings takes place(Fig. 5).

Except from very low gamma readings at Bastrup

and Addit Mark, the lower part of sequence D is char-acterised by very high gamma readings (Figs 5, 6).Ignoring these high gamma peaks (heavy minerals,seebelow),avery thin interval with increasing gammalog response is seen in the lower part of the sequence.The increasing gamma log readings correspond to ahighermud content of this part of the succession. Thisissucceededupwardsbyanoveralldecreasing gammalog trend, which is correlated to increasing sand con-tent (Fig.6).AtAdditMarkanabruptdecrease in gam-ma log response occur at 84 m (Fig. 6). This decreasereflects a sudden increase in the sand content. Up-wards a gentle increase in gamma log response char-acterise the upper part of the sequence. However,the maximum grain-size is seen at 58 m (Fig. 6). Southof Gram the sequence is dominated by mud (Fig. 5B).

Interpretation. The prominent change in gamma logresponse represents a change from marine to fluvialdeposits at Bastrup and Addit Mark (Karen Dybkjær,personal communication 2002) and thus representsa sequence boundary (e.g. Plint et al. 2001). In theStore Vorslunde borehole the change from an overallcoarsening upward section to a generally fining up-ward interval occurs at a gravel layer. The gravel isconcentrated within a thin layer and the grains areangular. This is interpreted as an indication of aravinement surface and the sequence boundary isplacedat the base of the gravel layer. Thick lowstand/transgressive deposits are found at Bastrup andAddit Mark. The transgressive systems tract in theother boreholes is very thin and the maximum flood-ing surface corresponds to the change from the fin-ing upward trend of the gamma log readings to anoverall coarsening upward trend. It is not placed atany of the extreme gamma log peaks, which corre-sponds to heavy minerals. From heavy mineral ex-ploitation it was found that there are two facies as-sociations: 1) a lower shoreface association with fine-grained, immature heavy minerals deposited instorm beds, and 2) a beach association with mature,medium-grained heavy minerals deposited in theswash zone (Knudsen 1998). These facies associationswere laid down during progradation of a shoreface.The highstand systems tract is, as described above,characterised by normal progradation of a shoreline.The upper part of the sequence at Addit Mark, wherean abrupt increase in the sand content occurs, is in-terpreted as a result of a sudden increase in sedimentsupply in to the area (Milana & Tietze 2002) possiblydue to tectonic movements (Koch 1989; Rasmussen2004).Fluvialdeposits which correlates with the pene-trated succession are exposed at the nearby sand pitat Addit Mark. Here the section is interpreted as flu-vial sediments deposited in a braided river system

99

referred to the Odderup Formation (Hansen 1985).The overall stacking pattern of the Odderup Forma-tion in the Addit Mark area is that of a progradationalunit succeeded by an aggradational unit capped bya retrogradational unit (Jesse 1995). The two lowerunits probably correlate with the highstand systemstract of this study.

Sequence E

Description. In most places the sequence boundary isplaced where lowest gamma readings are found (Figs5, 6). At Bastrup and Addit Mark the boundary isplaced where a decrease in gamma log response oc-curs above the most coarse-grained sediments (Figs5, 6).

Sequence E is characterised by an overall increas-ing gamma log response, especially at Rurup (Fig.5A). This increase in gamma log response correlateswith an increase in the content of mud and glaucony.The upper part of the sequence is characterised by arelatively thin interval of decreasing gamma log read-ings. Goethite-rich, silty sediments dominate this partof the sequence.

Interpretation. The depositional environment of thelowermost part of Sequence E varies laterally fromfluvial deposition (e.g. at Bastrup and Addit Mark)to marine offshore environment elsewhere (Fig. 5A).The sequence boundary corresponds to a major trans-gression recognised in the North Sea area and corre-lates with the Mid-Miocene unconformity (e.g. Huuse& Clausen 2001). The lower part of the sequence re-flects a major transgression, which culminated withthe deposition of glaucony-rich sediments. The over-lying goethite-rich silt is interpreted as deposited inshallower marine water (Dinesen 1976) and thus rep-resent the forced regressive wedge systems tract ofsequence E.

Sequence F

Description. The sequence boundary of sequence Fcannot be recognised on gamma logs. Instead, thisboundary is characterised by a distinct change in li-thology from silty goethite-rich deposits to clay-richdeposits as recognised in boreholes at Gram (Dinesen1976).

The gamma log response of this sequence shows agenerally decreasing log pattern. In boreholes andoutcrops the lower part of the succession is charac-terised by clayey deposits, which become more siltyupwards. A few thin, fine-grained, wave rippled sand

beds are found in the uppermost most part of thesuccession (Rasmussen & Larsen 1989).

Sequence F is characterised by a distinct upwardchangefrom silty clay or fine micaceous sand to chert-rich, often conglomeratic sediments. Sequence F istruncated by an erosional surface with strong reliefforming the boundary to the overlying Quaternarydeposits (Fig. 5).

Interpretation. The sequence boundary towards E isplaced above the goethite-rich deposits as these werelaid down during falling sea level (Dinesen 1976). Se-quence F was deposited in a marine environment andrepresentsan overall progradation of a shoreline (Ras-mussen 1961; Rasmussen & Larsen 1989). Sedimentsin the lower part of this sequence were deposited inabout 50 m of water (Rasmussen 1966) and the sedi-ments in the upper part in about 20 m of water (Ras-mussen & Larsen 1989).

PalaeogeographyBased on the sequence stratigraphic interpretation,a palaeogeographic reconstruction of the uppermostOligocene – Miocene succession in western Denmarkhas been developed (Fig. 7).

The trend of the shoreline was WNW–ESE and lo-cated in the northern part of the study area duringthelateChattian (latest Oligocene; Fig. 7A). The shore-line was characterised by barrier islands and associ-ated lagoons, which were connected with a majordelta located west of the study area (Huuse & Clau-sen 2001). In the marine realm, a very low sedimentinflux permitted the formation of glaucony both as-sociated with pellets and foraminifera (Rasmussen1996). A major displacement of the shoreline towardsthe south-west occurred during latest Chattian andthe shoreline migrated south of the Ringkøbing–FynHigh (Fig. 7B). Intensive formation of the autigenicmineral siderite and weathering of glaucony to goe-thite took place during this period of subaerial ex-posure, and is similar to the Recent Skjern Å delta(Postma 1982). Fluvial systems were probably con-fined to the topographic low of the Brande Trough.South of the Ringkøbing–Fyn High open marine con-ditions prevailed and nearshore marine sand wasdeposited along the high.

During the subsequent sea-level rise in the earlyAquitanian (Early Miocene), the area north of the el-evated part of the Ringkøbing–Fyn High formed amajor silled basin dominated by brackish water (Fig.7C). Parts of the nearshore sand deposited along theRingkøbing–Fyn High was redeposited as tempestites



E

J

Deltaic and continental deposits Beach deposits Lagoonal deposits Marine deposits

CHATTIAN CHATTIANSequence boundary B

AQUITANIANTST, LST sequence B(Vejle Fjord Clay/Sand)

AQUITANIANTST, HST sequence B

(Hvidbjerg sand)

AQUITANIANLST sequence C

(Ribe Fm.)

BURDIGALIANTST sequence C

BURDIGALIANMFS sequence C

( Lower Arnum Fm.)

BURDIGALIAN LANGHIANSequence boundary E

(Odderup Fm.)

SERRAVALLIAN TORTONIAN HST sequence F

(Upper Gram Fm.)

Ringkøbing

Fyn

MFS sequence A(Brejning Clay Mbr.)

BURDIGALIANSequence boundary D

(Bastrup sand)

MFS sequence D(Upper Arnum Fm.)

Brand

eTr

ough

High

Ringkøbing

Fyn

High

A

Formationof

Siderite + Goethite

F

B C D

HG

I

MFS sequence E(Hodde/Gram Fm.)

K L

Fig. 7: Palaeogeographical maps showing distribution of depositional environments during latest Oligocene – Miocene time.

101

similar to washover fans of a barrier system andsandy storm deposits; e.g. hummocky cross-strati-fied sand beds (Rasmussen et al. 2002). Progradationof the shoreline occurred during the highstand of sealevel (sequence B) (Fig. 7D). The shoreline was domi-nated by spit systems formed in association withstructural highs. The main delta was located in thecentral part of the study area just north of the BrandeTrough (Fig. 7D).

A major south–westward displacement of theshoreline occurred during the late Aquitanian andfluvio-deltaic sediments were deposited (Fig. 7E).This progradation was associated with a major sea-level fall (cf. Prentice & Matthews 1988), which re-sulted in deposition of forced regressive wedge sys-tems tract (sequence B) and lowstand systems tract(sequence C). Resumed transgression occurred in themid–Burdigalian (Fig. 7F), and the shoreline was dis-placed towards the north-east (transgressive systemstractof sequence C).The influence of the Ringkøbing–Fyn High was low at this time and brackish waterconditions were associated with back barrier envi-ronments (Fig. 7G). A new progradation of the shore-line took place during the late Burdigalian (Fig. 7H).This regression did, however, not extent as far to thesouth-west as the older Aquitanian regression (se-quence C) and occurred without a major sea-levelfall (cf. Prentice & Matthews 1988; Zachos et al. 2001).Therefore, most of the progradation occurred dur-ing highstand of sea level.

InthelaterpartoftheBurdigalian, the area was onceagain flooded and open marine conditions prevailedin the south-western part of the study area (Fig. 7I).At the Burdigalian–Langhian (Early – Middle Mio-cene) boundary progradation resumed (Fig. 7J), andwas associated with the accumulation of widespreaddelta swamp deposits, especially in connection withlows formed by tectonic movements along the Ring-købing–Fyn High (Koch 1989).

The major sea-level rise in the early Langhian (cf.Prentice & Matthews 1988) resulted in a prominenttransgression, which continued during Langhian–Serravallian times (Fig. 7K). This contradicts an over-all climatic cooling during the Serravallian (Prentice& Matthews 1988; Zachos et al. 2001) and acceler-ated subsidence of the North Sea area is thereforesuggested to be an additional factor (Clausen et al.1999; Rasmussen 2002). Additionally, the trend of theshoreline changed to NNW–SSE, which probably wasa result of tectonic movements along the Fennoscan-dian Shield. Strong reworking of former coal-richdeposits during the transgression resulted in the de-position of very organic-rich sediments in the lowerpart of the transgressive systems tract of sequenceE.

The shoreline began to prograde towards the westagain during the Tortonian (Late Miocene; Fig. 7L).

Stratigraphic distribution oflithological unitsThis study demonstrates that the lithostratigraphy ofthe Danish Miocene succession is in need of revision.It is, however, beyond the scope of this study to de-fine new lithostratigraphic units but the distributionof sand-rich and clay-rich deposits within the presentlithostratigraphic framework is shown in Figure 8.

The lithostratigraphy presented here is based onthe sequence stratigraphic interpretation of newstratigraphic boreholes, seismic data, outcrops andpits in Jylland (Fig. 8).

The oldest unit investigated here is late Chattianin age (latest Oligocene) and belongs to the basalBrejning Clay Member of the Vejle Fjord Formation(Fig. 8; Larsen & Dinesen 1959). The precise age ofthe Vejle Fjord Clay Member and Vejle Fjord SandMember is most likely earliest Aquitanian (lowermostMiocene). The Vejle Fjord Formation is succeeded bythe sand- and gravel-rich Ribe Formation (Sorgen-frei 1958), which is of Aquitanian to early Burdiga-lian age. In the southern part of Jylland the fine-grai-ned deposits underlying the Ribe Formation are re-ferred to the Klintinghoved Formation (Sorgenfrei1940; Rasmussen 1961). The Ribe and Klintinghovedformations are overlain by the Arnum Formation(Sorgenfrei 1958; Rasmussen 1961). This formationis generally fine-grained, but in central Jylland a sand-rich section is intercalated in the Arnum Formation(Fig. 8). The Arnum Formation is of Burdigalian age(Piasecki 1980; Dybkjær et al. 1999). Above the ArnumFormation follows the sand- and lignite-rich Odde-rupFormation(Rasmussen1961).This formationisre-ferred to the uppermost Burdigalian – lowermostLanghian. The lignite-rich part of the Odderup For-mation has been referred to the Fasterholt Memberby Koch (1989). The Odderup Formation is succeededby the clayey and organic-rich Hodde Formation(Rasmussen 1961) of Langhian–Serravalian age (Pia-secki 1980). Finally, the Miocene succession is com-pleted by the Gram Formation of Serravalian–Torto-nian age. The Gram Formation forms an overall coar-sening upward succession terminated by the Gramsand.



? ?

Odderup Fm.

Brejning Clay Mbr.Brejning clay Mbr.

Arnum Fm.

Gram Fm.

Hodde Fm.

Vejle Fjord Clay Mbr.

Ribe Fm.

? Klintinghoved Fm. VFS

QUAT. HolocenePleistocene

PLIO

CEN

E L

E

Piacenzian

Zanclean

Messinian

TortonianL

SerravallianM

M I

O C

E N

E

N E

O G

E N

E

E

Chattian

Langhian

Burdigalian

Aquitanian

L

E RupelianO L

I G

O C

E N

E

28.5

23.8

20.5

16.4

14.8

11.2

Ma

0.01

1.8

3.6

7.1

5.3

P A

L A

E O

G E

N E

PERIOD

SW NE

EPOCH A G E L I T H O S T R A T I G R A P H Y

VFS= Vejle Fjord Sand Mbr. GS=Gram silt/sand

Marine silt and clay Fluvial and marine sand HiatusBrackish watersilt and clay

Quaternary erosion

Vejle Fjord Fm.Vejle Fjord Fm.Vejle Fjord Fm.

GS

Sequ

ence

s(t

his

stud

y)

F

E

D

C

B

A

Fasterholt Mbr.Fasterholt Mbr.

Brejning Clay Mbr.Brejning Clay Mbr.

? Linde Clay? Linde Clay

Viborg Fm.Viborg Fm.

Branden Fm. Branden Fm.

Coal

Brejning Clay Mbr.

Branden Fm.

? Linde Clay

Viborg Fm.

Fasterholt Mbr.

Fig. 8: Lithostratigraphy of the latest Oligocene – Miocene succession in Jylland. The Oligocene lithostratigraphic units: ViborgFormation, Linde Clay and Branden Formation are from Heilmann-Clausen (1995) and Dybkjær et al. (1999). The dating of thelithostratigraphic units indicated above are based on Piasecki (1980), Dybkjær et al. (1999, 2001) and Dybkjær & Rasmussen (2000)and correlated to the biostratigraphy of Hardenbol et al. (1998). The time scale is from Berggren et al. (1985a, b).

103

A

30

25

20

15

10

Olig

ocen

eL.

Mio

cene

M.M

ioce

neU

.Mio

cene

Seri

es

Stag

es

Ma

(Ber

ggre

n et

al.

1985

a, b

)Glacioeustacy (m)

(Prentice & Matthews 1988)(Zachos et. al 2001)

Cha

ttia

nA

quita

n-ia

nBu

rdig

alia

nSe

rrav

allia

n

Messinian

Tort

onia

n

Langhian

Infe

rred

gla

cial

max

(Mill

eret

al.

1991

)

Tect

onic

eve

nts

Sequ

ence

s( t

his

stud

y)

BC

old

War

m t

emp.

Subt

ropi

c

Clim

atic

cha

nges

in C

entr

al E

urop

ae(L

otsc

h 19

68)

0

-20 20 40-40

-60

-80

-120

-140

-160

-100

Mi-1a

Mi-1

Mi-2

Mi-1b

Mi-7

Mi-6

Mi-5

Mi-4Mi-3

?

Subs

iden

ce

?

C

D

E

F? ?

Low High S N

Fig. 9: Comparison of eustatic sea-level curves, climatical changes, glacial maxima, tectonic pulses, and age of the sequencesrecognised in this study.

Allochtonous control on sequencedevelopmentClimatic control

Several studies of the Cenozoic succession of the east-ern North Sea area have revealed that close relation-ships existed between the development of the sedi-mentation and changes in eustatic sea level (Rasmus-sen 1996; Michelsen et al. 1998; Huuse & Clausen2001). In the following, the development of the se-quences defined in this study are compared withglacio-eustatic sea-level changes as indicated from

oxygen isotope studies and palaeoclimatical changesestimated from marine faunas and terrestrial floras(Fig. 9).

The data suggest that climatic changes occurredthroughout the latest Oligocene – Miocene time (Fig.9). The correlation between the different curves isgood and the period of changes varies between 2 Maand 4 Ma. In Central Europe variations from coldtemperate climates to subtropical climates occurred.This is in good agreement with the study by Buchardt(1978) for the North Sea.

The variation of sea level at the end of the Olig-ocene is only represented by the curve of Zachos etal. (2001). The deposition of sequence A coeval with



a sea-level rise within the Late Oligocene as indicatedby the glacio-eustatic curve. This is followed by asea-level fall, which relates to the glacial maximumMi-1 (Fig. 9). The deposition of sequence B mainlyfalls in between the two glacial maxima of Mi-1 andMi-1a, and corresponds to a period of higher sea level(Fig. 9). The coldest period occurred during the Aqui-tanian – early Burdigalian (Fig. 9) and is coeval withto the development of sequence boundary betweenB and C. This boundary is the most distinct sequenceboundary found in the region (Rasmussen 1996, 1998,2002) showing a well-developed forced regressivewedge systems tract and lowstand systems tract. Thefollowing general sea-level rise and overall transgres-sion during the Burdigalian is seen from the generalbackstepping stacking pattern of sequences C and Daccompaniedbydecreasingincision.Sequence bound-ary D probably formed during the glacial maximumMi-1b and a cooler period in the late Burdigalian (Fig.9). The development of sequence D occurred mainlyduring high sea level, which may explain the exten-sive deposition of lignite within this sequence. A dis-tinct general glacio-eustatic sea-level rise during thelate Langhian, as indicated on the curve of Prentice& Matthews (1988) (Fig. 9), is in good agreement withthe change from dominantly nearshore and terres-trial deposition of sequence D to open marine sedi-mentation dominating sequence E. However, neither

the curve from the continental climate nor the gla-cial maxima indicate a warmer period during theSerravallian. The timing of sequence boundary F cor-relates, however, to a cooler period in the Serraval-lian and Mi-5. A general fall in sea level and coolerclimatic conditions in the Tortonian (Fig. 9) is reflect-edintheoverallregressionfoundin the succession andparticularly demonstrated by the distinct prograda-tion seen in the Pliocene succession (Gregersen et al.1998).

The climatic influence on the development of thestudied succession is obvious, which of course shouldbe expected during this part of the Cenozoic, whenthe extent of polar ice caps were increasing (Prentice& Matthews 1988; Miller et al. 1991; Abreu & Ander-son 1998). However, the marked progradation seenwithin sequence D, and the overall transgression re-flected by the deposits of sequences E and F cannotreadily be correlated with climatically induced sea-level changes.

Tectonic influence

Four tectonic events during the Oligocene–Miocenehave been recognised from seismic mapping, stud-ies of sedimentary structures in outcrops, and frompalynological studies (Fig. 9).

The earliest tectonic event was in the beginning oftheChattian.Thisphase,knownasthe‘Savische Phase’(Fig. 9; Lotsch 1968), is well known in Central Eu-rope and is also recognised on seismic data from theeastern North Sea area (e.g. Clausen et al. 2000).

The second tectonic phase indicated in the upper-most Chattian is, however, uncertain. Convolute bed-ding and synsedimentary listric faults have been de-scribed from outcrops in eastern Jylland, which mayhave been caused by earthquakes (Mikkelsen 1983;Rasmussen & Dybkjær 1999).

An abrupt occurrence of reworked Jurassic sporesand pollen and high amounts of Paleocene and Eo-cene dinoflagellates within the upper Burdigaliansediments reflect the third tectonic event (Dybkjæret al. 2001). Above this level, a distinct regional in-crease in heavy minerals is observed in the Miocenesediments. Furthermore a marked thickening of theArnum Formation adjacent to the Tønder salt struc-tures (below the Tønder-3 well), suggests that saltmovements were active at this time (Fig. 10).

The fourth tectonic event in the Langhian (Fig. 9)is suggested by faults within the Odderup Forma-tion as seen in brown coal pits in central Jylland (Koch1989). These faults do not continue into the overly-ing late Langhian–Serravallian Hodde Formation.Furthermore, a tectonic reorganisation in the mid-

50 m

Tøn

der-

3

Borg

-1 Brøn

s-1

Løgu

mkl

oste

r-1

MFS

Fig. 10: Gamma log correlation of four boreholes in southernJylland. Movement of Zechstein salt during the late Burdiga-lian is reflected by marked thickness variation of the upperpart of the Arnum Formation (shaded). See Figure 3 for loca-tion of boreholes.

105

Miocene is also suggested by the cessation of majorsouth-westward progradation from the Fennoscan-dian Shield and the initiation of major westward pro-gradation from the Baltic and eastern European plat-forms during Late Miocene – Pliocene times (Clau-sen et al. 1999). This marked shift in source area can-not solely be attributed to eustatic sea-level changesor global climatical change, since this should haveproduced basin-wide progradation.

Studies of outcrops (e.g. Larsen & Dinesen 1959;Radwanski et al. 1975; Rasmussen 1987) and investi-gations of shallow boreholes in Jylland support theinterpretation of tectonic movements in the hinter-land during this time. The shallow marine depositsare composed of immature sediments apart fromsediments that accumulated in the swash zone of abeach. The quartz grains found within the fluvial de-posits are angular indicating that the newly exposedbasement became eroded. The Miocene fluvial de-posits were laid down by braided river systems(Hansen 1985), which do not favour a low relief hin-terland and tectonic quiescence during deposition assuggested by Huuse & Clausen (2001). Many stud-ies have shown a relationship between river patternand tectonics (Miall 1996 and references therein),which is similar to the pattern of the fluvial systemsand salt structures in central Jylland. Alternatively,the dominance of braided river systems of the Odde-rup Formation may have been a result of high sedi-ment supply caused by the increased erosion of thehinterland. The close relationship between the de-positionandpreservationofbrowncoal and fault pat-tern in central Jylland (Koch 1989) also supports theidea that tectonic disturbance was active at this time.

The four tectonic events discussed above corre-late well with the timing of pulses in the AlpineOrogen (Ziegler 1991; Ribeiro et al. 1990) and thetheory of intraplate stress (Cloetingh 1988) and theconsequences on depositional system are thereforeinteresting for the studied succession. The tectonicevents are, however, of a lower frequency than theclimatically induced cycles, but the interaction of tec-tonic and climatic processes is a likely explanationfor the evolution of the uppermost Oligocene – Mio-cene succession.

Sediment supply

The influx of sediments during the Oligocene andmost of the Miocene came from the FennoscandianShield (Larsen & Dinesen 1959; Spjeldnæs 1975; Mi-chelsen et al. 1998; Gregersen et al. 1998; Rasmussen& Dybkjær 1999). Progradational features have beenrecognised on seismic data from the North Sea south

of the Norwegian coast. Much of the sediment con-tains feldspar, angular quartz grains, and gibbsite andare interpreted as immature (Larsen & Dinesen 1959;Radwanski et al. 1975; Rasmussen 1987). This indi-cates that sediment transport was relatively fast andfrom newly exposed basement. The highest input ofsediment was from the area south of present-dayNorway with a minor supply from central Sweden.The topography of the North Sea area, which reflect-ed both regional tectonism and salt movements, in-fluenced the deposits with respect to both transportpathways and deposition. Especially, topographiclows on the Ringkøbing–Fyn High acted as conduitsfor sediments during lowstand of sea level in theEarly Miocene.

A distinct change to a westerly transport direc-tion occurred in the Middle Miocene with a sourcein present-day southern Sweden and the Baltic area(Clausen et al. 1999). The change was probablytectonically induced by the formation of the SouthScandic Dome (Lidmar-Bergstrøm 1996; Japsen &Bidstrup 2000). Kaolinitic Pliocene deposits in north-ern Germany reveal erosion of weathered basementin the hinterland and thus support the hypothesis oftectonic movements in southern Scandinavia in Mio-cene times (Lidmar-Bergstrøm 1996; Japsen &Bidstrup 2000).

Discussion and conclusionsJordt et al. (1995), Michelsen et al. (1998) and Huuse& Clausen (2001) have identified both 2nd and 3rdorder sequences in the Cenozoic succession from theNorth Sea area. These studies are mainly based onseismic data and petrophysical logs, mainly gammalogs. Sidewall cores and cuttings have also been usedin the study. The stratigraphic resolution is, however,considerably lower than for the data used in the pre-sent study in which the use of outcrops, stratigraphicboreholes, shallow seismic data and biostratigraphybased on high sample rates revealed six depositionalsequences in the uppermost Oligocene – Miocene suc-cession.

Most of the major sequence boundaries of Jordt etal. (1995), Michelsen et al. (1998) and Huuse & Clau-sen (2001) can be correlated with sequence bounda-ries of this study (Fig. 11). The base of sequence Acorresponds to the major sequence boundary 4/5 ofMichelsen et al. (1998) and to the seismic sequenceboundary Css4/Css5 and the near-top Oligocene ho-rizon of Jordt et al. (1995) and Huuse & Clausen(2001), respectively (Fig. 11).

Correlation from the Frida-1 well in the Danish



North Sea to this type section (based on dinoflagel-late cysts) has shown that the base of sequence A isof latest Late Oligocene (Fig. 11; Dybkjær 2004). Thenext major sequence boundary (5/6 and Css5/Css6)recognised by Michelsen et al. (1998) and Jordt et al.(1995) correlates with sequence boundary C of thisstudy. This sequence boundary is one of the most pro-nounced in the onshore area associated with the de-

position of the Ribe Formation (Forced regressivesystems tract of sequence B and lowstand systemstract of sequence C) and formerly described by Ras-mussen (1998). The third major sequence boundaryis the so-called mid-Miocene unconformity (sequenceboundary 6/7 and Css6/Css7) known from the NorthSea area (Jordt et al. 1995; Michelsen et al. 1998; Huuse& Clausen 2001) that is correlated with the sequenceboundary E of this study. The onshore developmentabove this boundary is that of a regional floodingand a change from predominantly shallow marineand terrestrial deposition that dominated during theEarly Miocene to open marine shelf deposition dur-ing the Middle and Late Miocene. This relative sea-level rise has been suggested to be controlled eitherby tectonic movements and increased subsidence(Jordt et al. 1995; Michelsen et al.1998; Clausen et al.1999; Rasmussen 2002) or by climatic changes (Huuse& Clausen 2001). A pure climatic control on the de-velopment of this sequence boundary is unlikely sinceit is developed as an overall transgressive event dur-ing relative sea-level fall (Zachos et al. 2001; Rasmus-sen 2004). Consequently, the most likely explanationfor the development of sequences E and F is a com-binationofclimaticvariationandtectonic movements.

Huuse & Clausen (2001) made a clear conclusionabout the origin of the sequences without recognis-ing the major sequence boundary C within the earlyBurdigalian, which correlates to the most distinct cli-matic change recorded in the Miocene (Prentice &Matthews 1988; Mai 1967; Lotsch 1968; Zachos et al.2001). However, this sequence boundary is the mostdistinct boundary in the onshore area showing all ofthe characteristics of classical systems tracts associ-ated with falling sea level and lowstand of the sea(e.g. forced regressive wedge systems tract andlowstand systems tract; Rasmussen 1998). Similarly,sequence boundary D shows both incision and de-position of lowstand deposits. These boundaries havenot been recognised by the studies based on seismicdata from the North Sea area (Jordt et al. 1995; Huuse& Clausen 2001). An explanation for this could bethat studies based mainly on seismic data in mostcases recognise major flooding events such as the lateOligocene and mid-Miocene (intra Langhian) sea-level rises (Fig. 9). Major flooding will often result invery different lithologies below and above a bound-ary, e.g. marine clay occurs above nearshore fluvialsand and gravel. Sequence boundaries formed dueto a marked lowering of base level, which are oftencharacterised by truncation surfaces, coarse-grainedlag deposits and sand to sand contacts, are poor seis-mic markers and therefore difficult to identify espe-cially on the relatively low-resolution data in theNorth Sea.

A

3

4

1

1

2

3

1

2

23

4

30

25

20

15

10

Olig

ocen

eL.

Mio

cene

M.M

ioce

neU

.Mio

cene

Seri

es

Stag

es

(Be

rggr

en e

t al. 1

985

a, b)

Cha

ttia

n

Css

4C

ss 5

Css

6C

ss 7

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Fig. 11: Timing of sequences of this study compared to studiesby Michelsen et al. (1998), Jordt et al. (1995), and Huuse & Clau-sen (2001). NTO: Near Top Oligocene and MMU: Mid-Mio-cene Unconformity. In this study, biostratigraphic data fromthe Oligocene–Miocene boundary type section in the Lemme–Carrosio section in northern Italy (Zevenboom et al. 1994) havebeen used to constrain the age of sequence boundary A, whichtherefore appears younger than shown in previous studies.

107

This study shows that both climatic changes andregional tectonic events play a major role in the de-velopment of the sequences. The tectonic events re-vealed by this study correlate with the major tectonicphases of the Alpine Orogeny (Fig. 9) and also tomovements associated with the opening of the NorthAtlantic, although the dating of the latter is less con-strained (Boldreel & Andersen 1993; Roberts et al.1999). The development of the sequences was partlycontrolled by structural highs especially in the lowerpart of the succession due to the topography formedduring the ‘Savische’ tectonic phase and at the endof the Burdigalian, corresponding to the Betic tec-tonic event. These structural elements partly control-led the distribution of open marine conditions andpartly the concentration of sand on the crests of struc-tural highs similarly to the Lower Cretaceous of Born-holm (Noe-Nygaard & Surlyk 1988).

AcknowledgementThe author is indebted to the Carlsberg Foundationfor financial support to the project and to the coun-ties in Jylland for access to data. Stefan Piasecki andKaren Dybkjær are acknowledged for their co-op-eration and valuable comments on the manuscript.Eva Melskens is acknowledged for preparation of thefigures. William Harrar improved the English.Thanks are due to Gunver K. Pedersen, Ole V. Vejbæk,Martin Sønderholm and Svend Stouge for construc-tive criticism and valuable comments on the manu-script.

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